[hackers] [scroll] Support scroll back after clear screen || Jochen Sprickerhof

[git]

commit 177976ae00fc60658c6f21739a3fd2462a02917f
Author:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
AuthorDate: Wed Apr 15 22:38:16 2020 +0200
Commit:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
CommitDate: Wed Apr 15 22:40:24 2020 +0200

    Support scroll back after clear screen

diff --git a/TODO b/TODO
index 8eeefb4..84ffd33 100644
--- a/TODO
+++ b/TODO
@@ -1,4 +1,3 @@
  * strlen function which is aware of unicode
  * handle wrapping lines in scrolling line count correctly
  * hotkey to dump buffer to file (like screen hardcopy)
- * scroll back if screen was cleared (sh; ls; clear; scrollup())
diff --git a/scroll.c b/scroll.c
index 5752cf8..dd44d8d 100644
--- a/scroll.c
+++ b/scroll.c
@@ -250,6 +250,16 @@ skipesc(char c)
        return altscreen;
 }
 
+void
+getcursorposition(int *x, int *y)
+{
+       char input[BUFSIZ];
+       write(STDOUT_FILENO, "\033[6n", 4);
+       ssize_t n = read(STDIN_FILENO, input, sizeof(input)-1);
+       input[n] = '\0';
+       sscanf(input, "\033[%d;%dR", x, y);
+}
+
 void
 addline(char *buf, size_t size)
 {
@@ -268,11 +278,13 @@ addline(char *buf, size_t size)
 void
 redraw()
 {
-       int rows = 0;
+       int rows = 0, x, y;
+
+       getcursorposition(&x, &y);
 
        /* wind back bottom pointer by one page */
        for (; bottom != NULL && TAILQ_NEXT(bottom, entries) != NULL &&
-           rows < ws.ws_row; rows++)
+           rows < x - 1; rows++)
                bottom = TAILQ_NEXT(bottom, entries);
 
        if (rows == 0)
@@ -298,18 +310,20 @@ redraw()
 void
 scrollup(int n)
 {
-       int rows = 2;
+       int rows = 2, x, y;
        struct line *scrollend = bottom;
 
+       getcursorposition(&x, &y);
+
        if (n < 0) /* scroll by fraction of ws.ws_row, but at least one line */
                n = ws.ws_row > (-n) ? ws.ws_row / (-n) : 1;
 
        /* wind back scrollend pointer by one page plus n */
        for (; scrollend != NULL && TAILQ_NEXT(scrollend, entries) != NULL &&
-           rows < ws.ws_row + n; rows++)
+           rows < x + n; rows++)
                scrollend = TAILQ_NEXT(scrollend, entries);
 
-       rows -= ws.ws_row;
+       rows -= x;
 
        if (rows <= 0)
                return;
@@ -334,8 +348,8 @@ scrollup(int n)
                bottom = TAILQ_NEXT(bottom, entries);
                write(STDOUT_FILENO, scrollend->buf, scrollend->size);
        }
-       /* move cursor from line n to the bottom left corner */
-       dprintf(STDOUT_FILENO, "\033[%d;0H", ws.ws_row);
+       /* move cursor from line n to the old bottom position */
+       dprintf(STDOUT_FILENO, "\033[%d;0H", x);
 }
 
 void